1. Field of the Invention
The present invention relates generally to lighting devices for photo electric flaw detection apparatus and is directed more specifically to a lighting device that uses a ring shaped or circular light source.
2. Description of the Prior Art
Presently, containers made of glass, plastic or the like as the main material have many purposes, such as for use in the bottling of pharmaceuticals, spirits or liquors, cosmetics, beverages and drinks, etc. One problem that rises during the production of such container, particularly bottles, during the distribution and the marketing of the product is the tendency for flaws or breakages to occur at the bottle mouth. Such flaws or breakages at the bottle mouth create problems in capping the bottle, leakage during the filling processes, or during the distribution processes that can ultimately cause breakages of the bottles themselves, or even cause injuries to the users. This is especially significant where use if made of recycled bottles (so-called refillable bottles collected and repeatedly refilled) where the bottles may be subjected to more than several cycles of use. Therefore, the bottle makers or bottlers that wash such bottles and refill the bottles with liquids, conduct manual visual inspection in order to reject any defective bottles, especially those at the bottle mouth.
In recent years, automatic inspection devices for inspecting bottle mouths using optical means, electrical means or the like have been developed to release the manual bottle mouth inspection, and to save labor. These devices, for instance cause the object to be inspected to be illuminated from a light source and the reflected light sensed by photoelectric conversion means such as a photo cell, video camera or the like, so that any abnormal reflection of light as caused by any flaw, crack or damage is detected.
Various lighting arrangements have been proposed for such automatic inspection devices. In one such lighting arrangement, the circular edge portion of the bottle mouth is irradiated (whether this portion is damaged or not) by a ring shaped, i.e., annular lamp such as a circular florescent lamp. An example of the use of this type of lamp in a prior art automatic inspection system is shown in FIG. 1 where the ring shaped lamp 1 is placed generally in a horizontal plane, under which a bottle 2 is placed with its mouth 3 centered along the central axis Y--Y of the lamp 1. The inner diameter of the ring shaped lamp 1 is selected sufficiently larger than the outer diameter of the bottle mouth 3 of bottle 2 and a photoelectric conversion sensor 4 such as a television camera is located to the side of the lamp 1 opposite that of the bottle 2 such that its optical axis is generally aligned with the central axis Y--Y. The sensor 4 receives the light reflected from the bottle mouth 3 and generates corresponding electrical signals which are processed in an otherwise known type inspection section D as a processor (i.e., computer) to determine whether or not a damage or flaw exists on the bottle mouth 3.
The state of the incident light from ring shaped lamp 1 on the bottle mouth 3 in such aforementioned arrangement, as well as the state of the reflected light therefrom is explained in FIGS. 2A, 2B and 2C. In FIGS. 2A, 2B and 2C, the circular lamp 1 amd the sensor 4 are not shown, although the light radiating from the lamp 1 is illustrated by the lines a while their reflections are illustrated by the lines b. Those light rays a extending parallel to or at an acute angle to the axis Y--Y and incident on the curved surface 6 of the circumferential edges of the lip portion 5 of the bottle mouth 3, above the circle shown by a broken line 7 in FIG. 2B, are reflected upward in the direction b and are introduced into the sensor 4 which is located above the bottle mouth 3.
The line 7 lies on the transitional point below which the reflection of light from above or even horizontally is deflected downwardly and thus not capable of incidence on the sensor 4. Generally speaking, the light rays a emitted from the ring-shaped lamp 1 is equally incident on the peripheral edge portion of the bottle mouth 3. The light incident on the mouth 3 above the line 7 when there is no flaw or damage on the bottle mouth 3 is reflected as light b from the surface 6 and enters the sensor 4. In other words, even when there are no abnormalities such as damages or the like on the bottle mouth 3, a part of the light rays from the lamp 1 reflects from the bottle mouth 3 and such reflected light is always introduced into sensor 4. When, however, there is a flaw or damage in the bottle mouth 3, the reflected light becomes scattered and this scattered reflection is introduced into sensor 4 in addition to the aforementioned normal reflected light so that the sensor 4 (and hence the inspection device D) detects an increase or decrease in intensity by which the damage or flaw is recognized. That is to say that in the above mentioned prior art inspection devices, there is an amount of entirely unnecessary reflected light from the bottle mouth 3 always entering the sensor 4, as a result of which the damage or flaw detection sensitivity is low.
Further, depending upon the shape of bottle 2, particularly the shape of the bottle mouth 3, at the inner peripheral edge of bottle mouth 3, there is also an equivalent range of eitherside of the broken line 7, as shown on FIGS. 2B and 2C, causing the incident light near it to also send reflected light into the sensor 4, making the detection more difficult and thereby further lowering the detection sensitivity.
An arrangement attempting to circumvent the above mentioned disadvantages is shown on FIG. 3 wherein a lamp 8 is used that emits a spot like light beam illuminating a small portion of the bottle mouth 3, and the sensor 4 is placed so that it receives only the reflected light from this beam. In this case, unless the bottle mouth 3, which means the bottle itself is rotated, the entire inspection thereof cannot be made, so that an extra bottle rotation device becomes necessary. The arrangement is accompanied by the disadvantage that the inspection takes a longer time to be completed.